Field of the Invention
The present invention relates to an organic light-emitting diode (OLED) display and a method for manufacturing the same. More specifically, the present invention relates to an organic light-emitting diode display and a method for manufacturing the same that can reduce a number of mask processes.
Discussion of the Related Art
Recently, a variety of flat panel displays having reduced weight and volume, as compared to cathode ray tubes, have been developed. Such flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), electroluminescent devices (ELs) and the like.
ELs are classified into an inorganic EL and an organic light-emitting diode display. ELs are a self-emissive device, and as such, they have various advantages, such as fast response speed, high luminous efficiency and brightness and wide viewing angle.
FIG. 1 illustrates a structure of an organic light-emitting diode according to the related art. As show in FIG. 1, the organic light-emitting diode includes an organic electroluminescent compound layer, a cathode and an anode opposite to each other having the organic electroluminescent compound layer interposed therebetween. The organic electroluminescent compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL) and an electron injection layer (EIL).
The organic light-emitting diode emits light according to energy from excitons generated through a process in which holes and electrons injected from the anode and the cathode are recombined in the EML. An organic light-emitting diode display displays images by electrically controlling the quantity of light generated in the EML of the organic light-emitting diode as shown in FIG. 1.
Organic light-emitting diode (OLED) displays, which use the characteristics of such an organic light-emitting diode, can be classified into a passive matrix type organic light-emitting diode (PMOLED) display and an active matrix type organic light-emitting diode (AMOLED) display.
The AMOLED display displays images by controlling the amount of current flowing through organic light-emitting diodes using thin film transistors.
FIG. 2 is an equivalent circuit diagram illustrating a structure of one pixel of an AMOLED display, FIG. 3 is a plan view of a structure of one pixel of the AMOLED display, and FIG. 4 is a cross-sectional view illustrating a structure of one pixel of the AMOLED display, taken along line I-I′ of FIG. 3.
Referring to FIGS. 2 and 3, an AMOLED includes a switching thin film transistor ST, a driving thin film transistor DT connected to the switching thin film transistor ST and an organic light-emitting diode OLED in contact with the driving thin film transistor DT.
The switching thin film transistor ST is formed at an intersection of a scan line SL and a data line DL, and serves to select a pixel. The switching thin film transistor ST includes a gate electrode SG, a semiconductor layer SA, a source electrode SS and a drain electrode SD. The driving thin film transistor DT drives an organic light-emitting diode OLED of a pixel selected by the switching thin film transistor ST. The driving thin film transistor DT includes a gate electrode DG connected to the drain electrode SD of the switching thin film transistor ST, a semiconductor layer DA, a source electrode DS connected to a driving current line VDD and a drain electrode DD. The drain electrode DD of the driving thin film transistor DT is connected to an anode ANO of the organic light-emitting diode OLED.
More specifically, referring to FIG. 4, the gate electrodes SG and DG of the switching thin film transistor ST and the driving thin film transistor DT are formed on a substrate SUB of the AMOLED. A gate insulating layer GI is formed on the gate electrodes SG and DG. The semiconductor layers SA and DA are formed on portions of the gate insulating layer GI, which correspond to the gate electrodes SG and DG. The source electrode SS and the drain electrode SD are formed on the semiconductor layer SA, opposite to each other having a predetermined gap provided therebetween. The source electrode DS and the drain electrode DD are formed on the semiconductor layer DA, opposite to each other having a predetermined gap provided therebetween. The drain electrode SD of the switching thin film transistor ST is connected to the gate electrode DG of the driving thin film transistor DT via a contact hole formed in the gate insulating layer GI. A passivation layer PAS is formed on the overall surface of the substrate so as to cover the switching thin film transistor ST and the driving thin film transistor DT having the aforementioned structure.
When the semiconductor layers SA and DA are formed of an oxide semiconductor material, a large-sized OLED display having high resolution, large charging capacity and fast driving speed can be achieved due to the oxide semiconductor's high mobility. The oxide semiconductor material layers may further include etch stoppers SE and DE for protecting the surfaces thereof from an etchant in order to ensure device stability. Specifically, the etch stoppers SE and DE are formed so as to reduce or prevent the semiconductor layers SA and DA from being back-etched due to an etchant contacting the exposed surfaces of the semiconductor layers SA and DA, which correspond to the gaps between the source electrodes SS and DS and the drain electrodes SD and DD.
A color filter CF is formed in a region corresponding to the anode ANO which will be formed later. The color filter CF is preferably formed to occupy a wide area if possible. For example, the color filter CF is formed such that the color filter CF is superposed on a wide area including the data line DL, driving current line VDD and scan line SL. The substrate on which the color filter CF has been formed typically has an uneven surface due to stepped portions since many components have been formed thereon. Accordingly, an overcoat layer OC is formed on the overall surface of the substrate in order to planarize the surface of the substrate.
Subsequently, the anode ANOP of the OLED is formed on the overcoat layer OC. Here, the anode ANO is connected to the drain electrode DD of the driving thin film transistor DT via a contact hole formed in the overcoat layer OC and the passivation layer PAS.
A bank pattern BN for defining a pixel region is formed on the switching thin film transistor ST, the driving thin film transistor DT and the interconnection lines DL, SL and VDD formed on the substrate on which the anode ANO is formed.
The anode ANO exposed through the bank pattern BN becomes an emission area. An organic emission layer OLE and a cathode layer CAT are sequentially formed on the anode ANO exposed through the bank pattern BN. When the organic emission layer OLE is formed of an organic material emitting a white light, the organic emission layer OLE expresses a color assigned to each pixel according to the color filter CF located under the organic emission layer OLE. In this manner, the OLED display is completed.
To manufacture such an OLED display, photolithography processes using photo-masks are performed multiple times. Each mask process typically includes cleaning, exposure, development, etching and the like.
When the number of mask processes increases, time and costs for manufacturing an OLED display and defect generation rate increase, thereby decreasing production yield. Accordingly, it would be beneficial to reduce the number of mask processes in order to decrease manufacturing costs and improve production yield and production efficiency.